Amorphous silicon is widely used in semiconductor devices, flat-panel displays, and solar cells. There remains a key technical challenge for the development of amorphous silicon deposition process with conformality (i.e., good step coverage) or gap-fill performance in high aspect-ratio features. Conventional LPCVD process is limited to high temperature (>550° C.) and low pressure, and, therefore, exhibits poor step coverage and/or gap-fill performance; PECVD process also does not give good step coverage and/or gap-full performance.
The atomic layer deposition (ALD) of tungsten thin films exhibits very long incubation delay's on silicon, silicon dioxide and titanium nitride services due to poor nucleation performance. A nucleation layer is usually used to mitigate this issue. Conventionally, ALD WSix or WBx is deposited by WF6/Si2H6 and WF6/B2H6, respectively. However, WF6 is directly exposed to the substrate surface (e.g., Si, SiO2) and damages the substrate.
Additionally, ALD tungsten films do not stick well directly on silicon or silicon oxide substrate surfaces. A titanium nitride glue layer is used to improve the adhesion. However, both the titanium nitride glue layer and WSix/WBx nucleation layer do not conduct well, resulting in a very high resistivity for the stack (W/WSix/TiN).
Therefore, there is a need in the art for methods of depositing metal films with high conformality.